The invention relates to a pipe line for an engine, in particular a cooling line for aircraft construction as well as a process for the manufacture of such pipe line.
The pipe line is fitted in the front region of the engine. Air under dynamic pressure is passed to the engine through the open end of the pipe line in order to cool the gears of the engine. Known pipe lines of this type are manfactured of high strength steels or titanium. Due to the dynamic loads resulting from the engine, the life expectancy of this component is limited.
Synthetic resins reinforced with high strength fibres and organic matrix materials such as epoxy or phenolic resins are used to an increasing extent because of their favourable mechanical properties and low mass as a replacement for light metal material such as aluminium or titanium, particularly in the aircraft industry. The range of usefulness of such synthetic resins in general has its maximum at about 180.degree. C. In the context of space travel and military aviation a special polyimide resin was developed which resists exposure to temperatures up to 400.degree. C. However, because of technological problems this synthetic resin cannot yet keep pace with the growth of the employment of fibre composite materials in the aircraft industry.
In the event of an engine catching fire, the pipe line of the gear mechanism of the engine must continue to supply cooling for a predetermined duration and must resist a predetermined internal pressure as laid down by the manufacturer of the engine.
To date such pipe lines have been manufactured of high temperature resistant steel. The operating temperature of the pipe line when starting the engine, amounts to 180.degree. to 280.degree. C. and reaches 370.degree. C. during long-term operation. In special situations such as fire, the temperature amounts to about 1100.degree. C. The pipe line must withstand this temperature for 15 minutes without burning through or leaking, whilst the mechanical strength as well must be preserved.
From DE-OS 26 25 107 a dual layer composite pipe of plastics is known, the inner layer of which is produced from a chemically and temperature resistant synthetic resin with a powderous and/or fibrous filler and the outer layer of which is produced of a reinforcing glass fibre reinforced synthetic resin, both layers being cured simultaneously under pressure and at elevated temperature.
CH-PS 623 908 describes a plastics pipe having an inner and an outer layer, each being glass fibre reinforced, the glass fibres in the inner layer being orientated circumferentially and in the outer layer axially in order to provide a high pressure resistance when used as a pipe for a natural gas pipe line. After the inner layer has been wound and cured on a pin, the pin is removed and replaced by a different one which generates an axial pressure. During the application and curing of the outer layer the inner layer is preferablly simultaneously subjected to the action of a pressure medium. In this case as well, it is apparent that the pin is only withdrawn after the outer layer has been cured to completion. The final curing takes place solely by increased temperature (infrared lamps).